procmailsc

```       [*] w^x condition

DESCRIPTION
In addition to the traditional true or false conditions you can specify
on a recipe, you can use a weighted scoring technique to  decide  if  a
certain  recipe  matches  or  not.   When weighted scoring is used in a
recipe, then the final score for that recipe must be positive for it to
match.

A  certain  condition  can contribute to the score if you allocate it a
`weight' (w) and an `exponent' (x).  You do this by preceding the  con-
dition (on the same line) with:
w^x
Whereas  both  w  and  x  are  real  numbers  between -2147483647.0 and
2147483647.0 inclusive.

Weighted regular expression conditions
The first time the regular expression is found, it will add  w  to  the
score.  The second time it is found, w*x will be added.  The third time
it is found, w*x*x will be added.  The  fourth  time  w*x*x*x  will  be

This can be described by the following concise formula:

n
n   k-1        x - 1
w * Sum x    = w * -------
k=1             x - 1

It represents the total added score for this condition if n matches are
found.

Note that the following case distinctions can be made:

x=0     Only the first match will contribute w to the score.  Any  sub-
sequent matches are ignored.

x=1     Every match will contribute the same w to the score.  The score
grows linearly with the number of matches found.

0<x<1   Every match will contribute less to the score than the previous
one.   The  score  will asymptotically approach a certain value
(see the NOTES section below).

1<x     Every match will contribute more to the score than the previous
one.  The score will grow exponentially.

x<0     Can be utilised to favour odd or even number of matches.

If the regular expression is negated (i.e., matches if it isn't found),
then n obviously can either be zero or one.

Weighted program conditions
If the program returns an exitcode of EXIT_SUCCESS (=0), then the total

will generate an additional score of:

x
/  M  \
w * | --- |
\  L  /

And:

* w^x  < L

will generate an additional score of:

x
/  L  \
w * | --- |
\  M  /

In  both  cases,  if  L=M, this will add w to the score.  In the former
case however, larger mails  will  be  favoured,  in  the  latter  case,
smaller  mails will be favoured.  Although x can be varied to fine-tune
the steepness of the function, typical usage sets x=1.

MISCELLANEOUS
You can query the final score of all the conditions on  a  recipe  from
the  environment  variable  \$=.   This  variable is set every time just
after procmail has parsed all conditions  on  a  recipe  (even  if  the
recipe is not being executed).

EXAMPLES
The following recipe will ditch all mails having more than 150 lines in
the body.  The first condition contains  an  empty  regular  expression
which,  because it always matches, is used to give our score a negative
offset.  The second condition then matches every line in the mail,  and
consumes  up the previous negative offset we gave (one point per line).
In the end, the score will only be positive if the mail contained  more
than 150 lines.

:0 Bh
* -150^0
*    1^1  ^.*\$
/dev/null

Suppose  you  have  a priority folder which you always read first.  The
next recipe picks out the priority mail and files them in this  special
folder.   The  first  condition is a regular one, i.e., it doesn't con-
tribute to the score, but simply has to be satisfied.  The other condi-
tions  describe  things  like:  john  and claire usually have something
important to say, meetings are usually important, replies are  favoured
a  bit,  mails  about Elvis (this is merely an example :-) are favoured
(the more he is mentioned, the more the mail is favoured, but the maxi-
mum  extra  score  due to Elvis will be 4000, no matter how often he is
mentioned), lots of quoted lines are disliked, smileys are  appreciated
*  300^0   ^Subject:.*Re:
* 1000^.75 elvis|presley
* -100^1   ^>
*  350^.9  :-\)
* -500^0   ^From:.*(boss|jane|henry)@work
* -100^3   > 2000
priority_folder

If you are subscribed to a mailinglist, and just would like to read the
quality mails, then the following recipes could do the trick.  First we
make  sure that the mail is coming from the mailinglist.  Then we check
if it is from certain persons of whom we value the opinion, or about  a
subject  we  absolutely  want to know everything about.  If it is, file
it.  Otherwise, check if the ratio of quoted lines to original lines is
at most 1:2.  If it exceeds that, ditch the mail.  Everything that sur-
vived the previous test, is filed.

:0
^From mailinglist-request@some.where
{
:0:
* ^(From:.*(paula|bill)|Subject:.*skiing)
mailinglist

:0 Bh
*  20^1 ^>
* -10^1 ^[^>]
/dev/null

:0:
mailinglist
}

For further examples you should look in the procmailex(5) man page.

CAVEATS
Because this speeds up the search by an order of magnitude,  the  proc-
mail internal egrep will always search for the leftmost shortest match,
unless it is determining what to assign to  MATCH,  in  which  case  it
searches  the  leftmost  longest match.  E.g. for the leftmost shortest
match, by itself, the regular expression:

.*     will always match a zero length string at the same spot.

.+     will always match one character (except newlines of course).

procmail(1), procmailrc(5), procmailex(5), sh(1), csh(1), egrep(1),
grep(1),

BUGS
If,  in  a  length condition, you specify an x that causes an overflow,
procmail is at the mercy of the pow(3) function  in  your  mathematical
library.
If in a regular expression weighted  formula  0<x<1,  the  total  added
score for this condition will asymptotically approach:

w
-------
1 - x

In order to reach half the maximum value you need

- ln 2
n = --------
ln x

matches.

AUTHORS
Stephen R. van den Berg
<srb@cuci.nl>
Philip A. Guenther
<guenther@sendmail.com>

BuGless                           2001/08/04                     PROCMAILSC(5)```